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    182 Nuclear fragmentation in protontherapy

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    Searches for axion-like particles via γγ\gamma \gamma fusion at future e+e\mathrm{e}^+\mathrm{e}^- colliders

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    Opportunities for searches for axion-like particles (ALPs) coupling to photons in e+e\mathrm{e}^+\mathrm{e}^- collisions at the Future Circular Collider (FCC-ee) and International Linear Collider (ILC) are investigated. We perform a study of the photon-fusion production of ALPs decaying into two photons, e+eγγe+  a(γγ)  e\mathrm{e}^+\mathrm{e}^- \overset{\gamma \gamma}{\longrightarrow} \mathrm{e}^{+}\;a(\gamma \gamma)\;\mathrm{e}^{-}, over the light-by-light continuum background, for the planned FCC-ee and ILC center-of-mass energies and integrated luminosities. An analysis of the feasibility measurements is presented using parametrized simulations for two types of detectors. Upper limits at 95% confidence level (CL) on the cross section for ALP production, σ(γγaγγ)\sigma(\gamma \gamma \to a \to \gamma \gamma), and on the ALP-photon coupling are obtained over the ma0.1m_a \approx 0.1--1000 GeV ALP mass range, and compared to current and future collider searches. Production cross sections down to σ(γγaγγ)1\sigma(\gamma \gamma \to a \to \gamma \gamma) \approx 1 fb (1 ab) will be probed at ma1m_a\approx 1 (300) GeV, corresponding to constraints on the axion-photon coupling as low as gaγγ2103g_\mathrm{a\gamma \gamma} \approx 2\cdot10^{-3} TeV1^{-1}